Pent roof information: structure, inclination and construction

Hardly any other roof seems as simple and easy as the pent roof. Despite this, or precisely because of this, it has proven to be extremely versatile in its use and at the same time adaptable to current requirements of all kinds. Everything you need to know about this interesting roof shape can be found below.

The emergence of the pent roof

Exactly when and where the pent roof was built cannot be reconstructed. Due to its simplicity, however, it must be assumed that it has existed for a very long time and that it probably arose independently in numerous places at the same time. If you look at illustrations from the Middle Ages and even antiquity, there are always buildings that at least suggest that they are covered with a pent roof.

Constructive features and static system

If we look at the construction of a pent roof, its structural simplicity quickly becomes the focus of attention. In general, as is the case with many other constructions, the supporting structure of the roof is formed by wooden rafters. These are placed on the outer walls of the building, with a base and a ridge sill forming the lower and upper supports. From a very large span of five meters between the walls, it is worth supporting the rafters at one or more points between the outer supports. Since all rafters are in one plane, the additional support points are usually replaced by a beam, i.e. a beam, to reduce the number of supports required further beams underneath at right angles to the rafters, or in the form of a wall with an overlying sill that is desired there anyway implemented.

Special shape sandwich roof

At this point, particular attention should be paid to the special case that the pent roof is not in is built in the form of a classic rafter construction, but created using sandwich elements becomes. A sandwich panel is a composite product of a load-bearing layer of sheet metal, a Insulation layer made of foamed plastic materials and a roof covering on the top made of one another sheet. Since load-bearing, insulating and sealing functions are combined in one component here, there is no need for structural support from rafters. Instead, the elements are placed directly on the required number of supports in the form of walls or beams.

The roof structure with sealing and insulation

However, the most common case with a pent roof is still the classic rafter construction. Therefore, a typical structure of a pent roof using a rafter system will now be explained as an example. From bottom (inside) to top (outside), the following layer structures result for a roof with thermal insulation inserted between the rafters:

• Lower clothing, e.g. B. Wood or plasterboard, on battens
• Vapor barrier as a diffusion-tight layer
• Rafter system with inserted thermal insulation, e.g. B. Mineral wool or cellulose insulation
• OPTIONAL: additional layer of insulation on the rafter layer, usually also effective as a watertight level
• Watertight level, usually in the form of a foil (unless provided with an additional insulation layer)
• Roof covering – see the following section for the different types of covering

Alternative structure with insulation layer on rafters (from bottom to top):

• rafter position
• Formwork made of gypsum fiber boards, wood etc.
• Diffusion-tight layer, e.g. B. as foil
• Insulation layer, either pressure-resistant as plastic foam, or soft as mineral wool or cellulose; in the case of soft insulation, joists are required as supporting structure roof covering
• Waterproof level, usually as a foil
• Roof covering - see next section

Roof coverings and slopes

While the actual roof structure is quite uniform, the actual roof covering and its substructure can differ greatly from roof to roof. Numerous variants are available for the pent roof:

Bricks and concrete roof tiles

Bricks and concrete roof tiles are identical in their use and function, but differ in the material used, clay or concrete. As a rule, they are applied to a two-layer substructure made of counter battens running from bottom to top and the actual supporting battens transverse to the direction of rise of the roof. The tiles or roof tiles are simply hooked into the battens with a lug on the back and, if necessary, fixed proportionately over the roof surface against strong wind suction with additional security.

• Minimum suitable inclination: usually 15 degrees, some types of bricks up to 10 degrees
• Maximum suitable inclination: depending on the type of tile and security, 45 degrees and more can easily be implemented, but then it usually no longer makes sense to have a pent roof

Foil or bituminous waterproofing

A homogeneous, flat roof covering is the version over roofing membranes on a foil basis, or as a bitumen-containing roofing membrane. Both differ in the type of materials, the bonding and the look. Otherwise, however, they can be considered identical.

1. With rear ventilation:

As a roof covering with rear ventilation, battens are applied to the waterproof level, which allows air to circulate to remove any moisture. This is followed by a supporting panel made of wood, to which the foil or bitumen roof is now applied.

2. Without rear ventilation:

Bitumen sheets or foil are applied directly to the insulation layer. There is no waterproof level below.

• Tilt: Both materials can be used anywhere from zero degrees

Covered with greenery / gravel

Neither a gravel roof nor a green roof are separate types of covering. Both coverings are based on a foil or bitumen roof. Often, however, these are provided with gravel or greenery, as both represent good ballast against wind suction and good protection against UV radiation and mechanical damage.

sheet

Finally, sheet metal is often found as a roof covering, especially on flat pent roofs. The tin roof requires the same substructure as the foil roof, but is normally only ventilated.

• Suitable slope minimum: 5 degrees
• Suitable slope maximum: unlimited

Roof structures and installations

Classic roof structures, such as dormers or roof cut balconies do not exist with the pent roof. In the case of steeply pitched pent roofs, skylights can sometimes be used, but skylights are more common for the predominantly fairly flat pitch. In many cases, however, such additional lighting and ventilation is completely dispensed with, since the pent roof favors the accommodation of normal facade windows in the vertical walls.

Costs

Although the real costs can of course only be determined with reference to a specific object, it can be said without considering individual cases that a pent roof is a very favorable roof shape. Since the roof consists of only one surface, expensive construction details are reduced to a minimum and special points such as ridges, ridges, valleys, etc. completely avoided. It is true that an equivalent roof space under your pent roof requires more external wall space than with a pitched roof example would be the case. However, this is offset by better usability thanks to vertical walls and fewer sloping ceilings. In general, it can be said without difficulty that the pent roof is the same as all others roof shapes clearly outperforms from an economic point of view.

Advantages and disadvantages

Numerous advantageous aspects of the pent roof are of course also faced with some disadvantages:

Advantages

• Good usability of the rooms below due to little sloping roof and missing gables
• Simple construction
• Thus: low susceptibility to damage due to a few, simple details
• Thus: low costs due to the lack of complex components
• Versatile in inclination
• Diverse visual design options
• Large roof area without changes in inclination or position, well suited for solar thermal or photovoltaics

Disadvantages

• Space in the upper attic area that cannot be used if there is a steep incline
• Simple optics, playful design is therefore usually difficult
• Very high wall height on the ridge side

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